Currently, prior art techniques to measure corrosion include either non-heat transfer methods, such as strip type or circular specimens, nipples, or changes in resistance of a thin metal tape or wire; or by heat transfer methods utilizing either single or multiple tube test exchangers. For non-heat transfer methods true conditions do not exist whereas for heat transfer methods actual velocity effect and/or surface temperatures are rarely identical, let alone provide accurate weight measurements.
In copending applications U.S. Ser. Nos. 202,351 now U.S. Pat. No. 4,339,945 and 202,352 now U.S. Pat. No. 4,346,587, assigned to the same assignee as the present invention and incorporated herein by reference, there are disclosed processes and apparatus for testing fluids for fouling characteristic. Fouling is an extremely complex phenomenon. From a fundamental point of view, it may be characterized as a combined momentum, heat and mass transfer problem. In many instances, chemcial reaction kinetics is involved, as well as solubility characteristics of salts in water and corrosion technology. It has been stated that if the fouling tendency of a cooling water can be accurately predicted before a plant is designed and built, significant capital savings might be realized through more accurate heat exchanger specifications.
As part of the process and apparatus, there is provided a heat transfer test assembly including a heat member for controlled heat input and thermocouples to measure wall temperatures of the heating member to permit fouling determinations at varying flow rates with simultaneous monitoring and recording thereof together with data, such as corrosion, pH, conductivity and the like. Measurement of corrosion is effected by a corrolator wherein current flow through an electrically conductive liquid is measured against a voltage drop.
Other methods of evaluating corrosion include (1) measurement of pit depth versus time and (2) visual interpretation of the percent of the corroded surface. The methods for evaluating corrosion heretofore used but do not actually measure corrosion or corrosion rate under controlled conditions of both the water film heat transfer coefficient as a function of velocity-caused shear effect, and surface temperature as a function of accurately controlled heat flux.